Carbon for benefit of the farmer

Summary

We investigated carbon storage, biological activity, soil structure and other physical soil conditions on 16 commercial farms in Norway with silty and sandy soils. In the last 20 years, these farms have had arable farming with annual soil tillage and no grass crops, or crop rotations with grassland included. Crop rotations with grassland and application of animal manure have been regarded as measures to enhance the content of organic matter and thus carbon storage in soil. However, few investigations have been done at farm level, particularly in silty and sandy soils where the carbon storage capacity are weaker than in clay soils. On the participating farms, soils were amended with mineral fertilizer and animal manure, mainly pig or cattle slurry. On each farm, two fields were chosen where cereals were grown in 2020. Per field, two sampling areas were selected where we investigated soil physical, biological, and chemical characteristics between August and October 2020, shortly after the cereal harvest.
We observed a clear trend with more organic carbon, better soil aggregate formation and aggregate stability, more rapid degradation of cotton cloth, tea-bags and straw and more earthworm numbers with grassland in the crop rotation. Some factors were not statistically significantly affected of crop rotation and fertilization assessed one by one, but the overall pattern clearly showed better soil conditions when grassland is included in crop rotation. We observed that fertilization with animal manure increased carbon storage, improved aggregate stability, and enhanced soil respiration on arable farms.
We recommend the spade as the best tool to judge soil structure, dense layers, root growth, content of earthworms and degradation of plant material from the previous season. This can be supplemented with various simple methods like burying a piece of cotton or a tea bag and examining how much is left a few months later. Penetrometer and infiltration measurements can provide valuable information, but moisture conditions and soil type must be carefully considered when evaluating the assessments.